WSU Extension


Crown gall 
European canker (Nectria canker) 
Fire blight 
Pacific Coast pear rust 
Pear trellis rust 
Powdery mildew 
Pseudomonas blossom blast and dieback 
Stony pit 
Virus diseases 
Apple-and-thorn skeletonizer 
Brown marmorated stink bug 
Codling moth 
Cutworms and armyworms 
Pear psylla 
Pear slug (pear sawfly) 
Pearleaf blister mite 
San Jose scale 
Spider mites 

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Caption: Pseudomonas cankers on pear twigs
Photo by: R.S. Byther
Pear : Pseudomonas blossom blast and dieback
(revision date: 4/11/2018)

Blossom blast and dieback is caused by a bacterial infection. The infection causes buds to turn a papery brown and die. Leaves may be spotted. Flower petals and stems may also be affected, and fruit cluster bases can turn brown or black. Occasionally, fruiting spurs may be killed. Cankers may develop in twigs and branches. Symptoms of this disease, especially on flowers, may closely resemble fire blight. However, blast infections seldom extend more than 1"-2" into a spur. Bacterial ooze, which is common with fire blight, is not present with Pseudomonas blast. Ornamental pears and most Asian pear cultivars are also susceptible. Frost and cold injury promote infection, which is common in cold, wet springs. Warm, dry weather inhibits disease.
Management Options

Non-Chemical Management
  • Prevent frost injury when possible. Plant hardy varieties in protected locations.
  • Asian pear cultivars 'Niitaka', 'Seigyoku', 'Shinseiki' and 'Shinsui' have intermediate resistance.
  • Prune out and destroy infected tissues as soon as they are noticed. Make cuts at least 6" below infected areas and sterilize pruning tools between cuts.
  • Provide proper culture to minimize amount of succulent shoot growth and to reduce injuries.
  • Avoid wounding plants.
Select non-chemical management options as your first choice!

Chemical Management

Apply before fall rains and again before spring growth starts. Excessive amounts may cause fruit russet. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Bonide Copper Fungicide Spray or Dust RTU [Organic]
    Active ingredient: basic copper sulfate  |  EPA reg no: 4-58
  • Bonide Liquid Copper Fungicide Conc/Organic Gardening
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-4
  • Soap-Shield Flowable Liquid Copper Fungicide [Organic]
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-56872
  • This list may not include all products registered for this use.

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Caption: Pseudomonas cankers on pear twigs
Photo by: R.S. Byther